The present invention relates to a biochemical sensor making use of an optical film, component members of such a sensor, and a measuring apparatus using the same.
Hitherto, labeling of radioactive or fluorescent substances has been resorted to for the measurement of binding of biochemical substances such as antigen-antibody reactions. This labeling, however, was time-consuming, and especially labeling of proteins was complex in its process and could cause a change of properties of the labeled protein.
A biochemical sensor making use of a change of interference color of an optical film is known as a means for the direct measurement of binding between biochemical substances with ease without resorting to labeling. Such a biochemical sensor is described in a paper by Sandestrom et al (Appl. Opt., 24, 472, 1985). An example thereof is here explained by referring to FIG. 1. A thin optical film 2 is provided on a substrate 1. Refractive index of the air is 1.00, so the optical film 2 is made of a material with a refractive index of 1.50 while the substrate 1 is made of a material whose refractive index is 2.25. When the optical film is designed to have a thickness which, in terms of optical length, is ¼ of wavelength λ0 of visible light or odd multiples thereof (such as ¾λ0 or 5/4λ0), the optical film functions as an antireflection film, and as shown in FIG. 2, intensity of the reflected light in the direction perpendicular to the optical film becomes 0 at wavelength λ0 as in the reflection spectrum A of FIG. 2. Consequently, the sensor produces an interference color. A monomolecular layer of the first biochemical substance 3 is provided on said optical film 2. In case the biochemical substance is protein, refractive index of the layer is about 1.5 and its thickness is around 10 nm. This optically represents an increase of thickness of the optical film, and the reflection spectrum changes from the solid line A to the dotted line A′ in FIG. 2, producing a corresponding change of interference color. When this first biochemical substance 3 is biochemically bound with a second biochemical substance 4, a further increase of film thickness is induced, providing a change from the dotted line A′ to the broken line A″ in FIG. 2 and a corresponding change of interference color. Thereby binding of the second biochemical substance is detected. In the ordinary procedure of detection, there is initially prepared a sample comprising a monomolecular layer 3 of a first biochemical substance covering optical film 2 on substrate 1. This sample is put into a solution of a second biochemical substance, then taken out from the solution and dried, after which the change of interference color from the dotted line A′ to the broken line A″ in FIG. 2 is examined. Thus, in the prior art, the sensor is taken out into the air and dried, and then interference color is determined.
According to the sensor described in the above paper, however, since the sensor is once taken out into the air and dried before determining interference color, time is taken for the drying step and a high throughput is hardly obtainable.
Further, since measurement is conducted after the passage of a predetermined period of time from start of the reaction, the sensor might be taken out into the air before the reaction is saturated, depending on the way of setting of the predetermined period of time, so that the measurement is not always accurate. On the other hand, when the predetermined period of time is set long to make sure that the measurement is made after the reaction has been sufficiently saturated, time efficiency is bad since the sensor is left immersed in the solution even after the reaction has been saturated.